Draw geometry on screen using BGL module
All the available OpenGL calls exposed in the bgl API are: https://www.blender.org/api/blender_python_api_current/bgl.html

(or in https://svn.blender.org/svnroot/bf-blender/trunk/blender/source/blender/python/generic/bgl.c without the gl prefix)

It has a few OpenGL 2.0 calls, but not even all I think.
It's easy to extend it to specific functions, but we are close to the point where it makes more sense to use a full OpenGL wrapper such as PyGL (and that's why the number of functions exposed is a bit stagnated).